The patent application US 2015/0021135 discloses a hydrodynamic torque converter comprising an impeller wheel intended to be coupled to a crankshaft and adapted to hydrokinetically rotate a turbine wheel, through a reactor. The impeller wheel is rotationally coupled to a cover wherein the impeller wheel, the turbine wheel and/or the damping means are at least partially accommodated. The turbine wheel is adapted to be axially moved between an engaged position in which the turbine wheel and the impeller wheel are axially moved closer to each other and rotationally coupled together, and a disengaged position in which the turbine wheel and the impeller wheel are axially moved away from each other and rotationally uncoupled.
The hydrodynamic torque coupling device further comprises a hub intended to be coupled to a transmission input shaft, connected to the turbine wheel through damping means.
The damping means comprise an annular wheel disc integral with the hub, two guiding washers axially positioned on either side of the annular wheel disc, and first elastic members acting on the circumference mounted between the annular wheel disc and the guiding washers. The first elastic members are adapted to act against the pivoting of the guiding washers relative to the annular wheel disc. The damping means further comprise second elastic members acting onto the circumference and mounted between a linking member attached to the turbine wheel and one of the guiding washers. The second elastic members are adapted to oppose the pivoting of the guiding washers relative to the turbine wheel.
In operation, in the disengaged position of the turbine wheel, the torque is transmitted from the crankshaft of the vehicle engine to the cover and to the impeller wheel, with such torque being then transmitted to the turbine wheel through the hydrokinetic coupling means formed by the impeller wheel, the turbine wheel and the reactor. The torque is then transmitted to the hub through the damping means.
When the turbine wheel is in the engaged position, the torque is directly transmitted from the cover and from the impeller wheel to the turbine wheel, without any action from the hydrokinetic coupling means. The torque is then transmitted to the hub through the damping means.
The turbine wheel moving between the engaged and disengaged positions thereof thus makes it possible to activate or deactivate the hydrokinetic coupling.
Additionally, the torque converter is adapted to operate in a so-called direct mode, wherein the torque is transmitted from the impeller wheel to the turbine wheel. More specifically, in the disengaged position of the turbine wheel, i.e. when the hydrokinetic coupling is activated, the impeller wheel turns faster than the turbine wheel. Conversely, in a so-called back operation, the turbine wheel can turn faster than the impeller wheel.
The back operation mode is used for instance when the motor brake is used or when the user suddenly takes his/her foot off the accelerator pedal.
In some operation cases, specifically in the back mode and when the hydrokinetic coupling is activated, the turbine wheel may be axially pushed back opposite the impeller wheel. It is important to limit such a motion of the turbine wheel so as to prevent a possible damage to the torque converter and to enable the motion of the turbine wheel to the engaged position thereof, if necessary.
In the torque converter disclosed in the patent application US 2015/0021135, the radially internal periphery of one of the guiding washers comprises a large rest area adapted to rest on a radial part of the cover, so as to limit the motion of the turbine wheel-damping means assembly.
In this embodiment, the turbine wheel indirectly axially rests on the radial part of the cover through a large number of parts. The accurate position of the turbine wheel is not easily controlled because of the dimension tolerance of each part belonging to the corresponding chain of dimensions.
Besides, the large area whereon the mentioned above guiding washer rests on the cover generates a significant frictional torque in operation.